I’m seeing that Minitel terminals are missing on MESS/MAME (and the closer we have there are home computers that could be used as Minitel terminals, which i think isn’t enough).How soon can we see them included?Thanks in advance!

If resources are available it will happen when somebody with an interest and knowledge of the code base finds time to do it. If resources aren't available, it's not going to happen.

As for remote servers shutting down, it's a real problem for many situations. Unless the remote server software can be found too it's simply not going to be the correct experience. MAME is going to need some kind of system to simulate server behavior for a lot of cases, provide simple basic responses to at least show the systems run, but a lot of the time you're going to end up with minimal functionality at best, just enough that the various codepaths in the rom for the system can be triggered.

Mind that all business logic is lost (and backups of real BTX pages in their original form, too).

Early BTX used Prestel-Minitel encoding on clients, so there are * some * similarities. O. Galibert noted Minitel also had 1200/75 baud modems. At a metered connection, it was an expensive and slow experience i wish i could forget